1. Field Of The Invention
The invention relates generally to container-filling-and-weighing devices, such as gross weigh auger baggers. The invention relates more specifically to the element or elements, and their configuration, used to measure the weight of a container filled by the filling and weighing device.
2. Description Of The Related Art
A conventional gross weigh auger bagger, which is one example of a container-filling-and-weighing device, is shown in FIG. 1, having a frame 2 to which a motor 4, auger 6 and hopper 8 are mounted. A weighing arm 10 is connected to the frame by load sensing devices, such as shear beam load cells 12, mounted between the top of the frame and the top of the weighing arm. A filling nozzle 14 extends from the auger over the weighing arm.
An outer tube 16 extends around the nozzle and rests against the top of the weighing arm. The outer tube and nozzle extend into a hole in the side of a bag, and fill the bag with particulate material forced through the nozzle by the auger. Any downward force exerted on the outer tube by the bag and its contents is directed onto the top of the weighing arm.
The bottom of the bag rests on a cantilevered platform 18 extending outwardly from the weighing arm. The weighing arm is weighted downwardly by the bag filled with particulate matter, and the downward force deflects the load cells, causing them to emit a signal or change characteristics in proportion to the force. The function of such a machine is to fill a bag while directing all the weight of the bag onto the load cells so that an accurate measurement of weight can be made during filling. The filling operation is then stopped when a predetermined weight of material has been deposited into the bag.
In existing machines, such as the one shown in FIG. 1, the position of the bag on the outer tube and the cantilevered platform affects the weight measurement. This results from the configuration of the machine, in which the downward (vertical) force applied by the bag and its contents is horizontally offset from the load cells. The downward force due to gravity that the bag applies to the outer tube of the nozzle and the cantilevered platform has a moment arm extending perpendicularly from the point where the force is applied (the nozzle and the cantilevered platform) to the point where the force is measured (the load cells). Placement of the bag on the nozzle and cantilevered platform creates a torque, which causes nonvertical forces to be applied to the load cells.
The nonvertical forces affect the weight measurement made by the load cells, since they affect the deflection of the load cells. When subsequently filled bags are placed on the machine at different distances from the load cells, moment arms of different length exist. As the moment arms vary, the nonvertical forces vary, and therefore the measured weights vary. This is so even if each of the bags has identical weight. If each bag were placed at exactly the same position on the nozzle and cantilevered platform, the nonvertical forces would be the same and could be neglected or electronically removed. However, in manufacturing facilities using these machines, placement of a bag in exactly the same position each time is impractical and rarely achievable.
In conventional machines such as the apparatus shown in FIG. 1, the load cell (or two load cells side by side) is positioned near the top of the weighing arm and a laterally flexible, longitudinally rigid plate is positioned near the bottom. The purpose of the flexible plate is to reduce the deflection of the load cells due to the nonvertical forces by permitting essentially free vertical translation (lateral flexure of the plate) and reducing horizontal displacement (compression along the length of the plate). However, in order for the flexible plate to eliminate most of the effect of the nonvertical forces, the plate must be perfectly parallel to the load cells. Even if the flexible plate is adjusted properly, it rapidly departs from its setting during operation.
Inaccuracies in most conventional machines range from several ounces to several pounds for a 50 pound bag. Therefore, the need exists for a significantly more accurate device connecting the weighing arm to the frame.